1. Technical Field
The present invention relates to a liquid ejecting apparatus such as an ink jet printer and a control method thereof, and particularly relates to a liquid ejecting apparatus that includes a liquid ejecting head in which a change in pressure is applied to a pressurizing chamber communicating with a nozzle, thereby causing liquid within the pressurizing chamber to be ejected from the nozzle, and to a control method for the apparatus.
2. Related Art
A liquid ejecting apparatus is an apparatus that includes a liquid ejecting head capable of ejecting a liquid, and that ejects various types of liquid from the liquid ejecting head. An image recording apparatus such as an ink jet printer (called simply a printer hereinafter) that is provided with an ink jet recording head (called simply a recording head hereinafter) as its liquid ejecting head and that records images by causing ink in liquid form to be ejected from a nozzle in the recording head and impact upon a recording medium such as a recording sheet (an impact target) may be given as a representative example of such a liquid ejecting apparatus. Meanwhile, in addition to such image recording apparatuses, liquid ejecting apparatuses are recently being applied in various manufacturing apparatuses, such as apparatuses for manufacturing color filters for liquid crystal displays and the like.
Some such liquid ejecting apparatuses are configured so that a change in pressure is applied to the liquid within the pressurizing chamber by applying a driving pulse (ejecting pulse) to a pressurizing element (for example, a piezoelectric vibrator, a heating element, or the like) and driving the element, using this change in pressure to cause liquid to be ejected from the nozzle that communicates with the pressurizing chamber. With such a liquid ejecting apparatus, the amount of ejected liquid may be increased by increasing the amplitude of the pressure oscillation applied to the liquid in the pressurizing chamber. To rephrase, the amount of ejected liquid may be increased by increasing the voltage of an ejection driving pulse (see, for example, JP-A-2003-94656).
Recently, attempts are being made to use such liquid ejecting apparatuses to eject liquids of a higher viscosity (called highly-viscous liquids hereinafter) than liquids handled in the past, such as, for example, UV ink (ultraviolet light-curable ink). In other words, although liquids having a low viscosity similar to water have been handled in the past, attempts are recently being made to eject highly-viscous liquids of 8 millipascals per second or more. In order to obtain a sufficient ejection amount when ejecting such highly-viscous liquids, it is necessary to apply, to the liquid within the pressurizing chamber, a pressure change adapted to the ejection amount. However, increasing the pressure change causes the liquid to travel at a higher speed, which tends to cause the occurrence of a phenomenon in which the posterior portion of the liquid extends in a tail-like form. Thus there has been a risk of this tail-like portion separating and jumping away from the primary droplet and failing to impact in the proper location (the desired location) on the impact target. For example, in ink jet printers, there has been a problem in that the tail-like portion has turned to mist, shifting from the proper location and then impacting, resulting in separated dots and thus leading to a degradation in image quality. In particular, with highly-viscous liquids, the tail-like portion separates into several parts, and those multiple separated parts (satellite ink droplets, or mist) have been the cause of a dramatic drop in image quality.
Therefore, a configuration has been proposed whereby a driving signal is provided with a driving pulse for reducing the aforementioned tail-like portion by quickly retracting the meniscus into the pressurizing chamber immediately after ink has been ejected. This driving pulse is, for example, a non-ejection driving pulse starting with a retracting element that retracts the meniscus by expanding the pressurizing chamber to a degree whereby ink is not discharged from the nozzle.
However, there is a risk that residual vibrations occurring in the ink within the pressurizing chamber due to the application of the non-ejection driving pulse to the pressurizing element will negatively influence the ejecting operations in the next ejection cycle (that is, cause changes in the ink amount, flight speed, and so on). Accordingly, it has been necessary to provide a period for dampening residual vibrations after the non-ejection driving pulse in order to suppress such negative influence. There has thus been a problem that the overall ejection cycle has been lengthened by the vibration dampening period, resulting in a drop in the drive frequency.